<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

    <style>
div {
    width: 100px;
    height: 100px;
    background-color: skyblue;
}

.change{
    background-color: purple;
    color: #fff;
    font-size: 30px;
    margin-top: 100px;
}
    </style>
</head>
<body>
    <div class="first">文本</div>
    <script>
// 1.element.style 获得修改元素行内样式
let div = document.querySelector('div');
div.onclick = function () {
      // div.style.color = '#fff';
        // div.style.fontSize = '30px';
        // div.style.marginTop = '100px';
        // div.style.backgroundColor = 'purple';

        // 2. 通过类名修改样式
        div.className = 'first change';
}
    </script>
</body>
</html>